The ocean surface is constantly in motion, and an ocean wave is fundamentally a disturbance that transfers energy through the water. Wave size is typically measured by its height, which is the vertical distance between the trough (the lowest point) and the crest (the highest point). The overall size of a wave is highly variable, determined by the source of the energy that creates it, which can range from a gentle breeze to a massive geological event.
The Mechanics of Maximum Wind Waves
The largest waves generated by the wind, often called surface gravity waves, depend on a perfect alignment of three primary factors. The first is wind speed, as faster winds transfer more energy to the water surface through friction, creating ripples that grow into larger waves.
The second factor is duration, meaning how long the wind blows across the water’s surface. A strong wind that only lasts a few minutes will not create the immense waves that a sustained storm can produce. The third factor is fetch, which is the uninterrupted distance over the water that the wind blows in a consistent direction.
The biggest wind waves, sometimes reaching a “fully developed sea” state, occur when all three conditions are maximized. This typically happens in powerful, long-lived storms far from land, such as those found in the vast Southern Ocean. When these factors combine, waves grow until the energy gained from the wind is balanced by the energy lost through breaking wave tops and turbulence.
Freak Waves and Theoretical Limits
Surface waves have a theoretical limit to their steepness before they become unstable and break, a concept known as the Stokes limit. This limit is reached when the ratio of wave height to wavelength is approximately one to seven (1:7). At this point, the wave crest forms a sharp, 120-degree angle, causing it to plunge forward.
This theoretical ceiling is occasionally shattered by the phenomenon known as a “rogue” or “freak” wave. These waves are defined not by their absolute height, but by their extreme size relative to the surrounding sea state, usually being more than twice the height of the average largest waves. Rogue waves are products of constructive interference.
Constructive interference happens when multiple smaller wave crests, traveling at different speeds and directions, momentarily align and combine their energy. This superposition creates a single, towering wall of water that appears and disappears quickly, often without warning. These unpredictable anomalies are distinct from wind-driven storm waves, which are more consistent and predictable.
Tsunami: The Biggest Waves by Volume
Tsunamis are fundamentally different from wind-generated waves because they are not caused by surface energy, but by massive displacement of water. The most common cause is a large-scale geological event, such as an undersea earthquake, volcanic eruption, or a massive landslide. This sudden movement vertically shifts the entire water column from the seafloor to the surface.
In the deep ocean, a tsunami typically travels at the speed of a jet plane but has an extremely long wavelength, sometimes over 100 miles from crest to crest. Due to this immense length, the wave’s height in the open sea is often less than one meter, making it virtually undetectable to ships. The sheer volume of water involved, however, contains tremendous energy.
The wave’s destructive potential only becomes apparent as it approaches the coast and enters shallow water. The decrease in water depth forces the wave to slow down, and the energy is compressed, causing the wave height to rapidly increase, a process called shoaling. The size distinction for a tsunami is measured by its “run-up,” which is the maximum vertical height the water reaches on the shore above the normal sea level.
Record-Breaking Waves and Measurement
The extremes of wave size are categorized by their formation mechanism, and records have been set across all types. The largest single wave ever documented was a mega-tsunami that occurred in Lituya Bay, Alaska, in 1958. An earthquake-triggered landslide sent approximately 90 million tons of rock into the narrow inlet, creating a massive splash wave that resulted in a run-up of 1,720 feet (524 meters), stripping the trees from the surrounding mountainside.
In the category of open-ocean rogue waves, the Draupner wave, recorded by a laser sensor on an oil platform in the North Sea on New Year’s Day 1995, is a significant landmark. This wave measured 84 feet (25.6 meters) from crest to trough in a sea state where the significant wave height was only about 39 feet (12 meters). More recently, the 2020 Ucluelet wave off the coast of British Columbia, while shorter at 58 feet (17.6 meters), was nearly three times the height of its surrounding waves, making it the most extreme rogue wave recorded relative to its peers.
These extremes are measured using a variety of sophisticated methods. Automated buoys and platforms use downward-pointing laser sensors and pressure sensors to provide accurate, real-time measurements of wave height and period. Satellite altimetry is also used to measure significant wave height over wide ocean areas, providing broader data on sea state conditions.